PHILOSOPHICAL SOCIETY OF WASHINGTON. 239 



Should any one be disposed to conclude that this simple ex- 

 tension of Schweigger's multiple coil was unimportant and un- 

 meritorious, the ready answer occurs, that talented and skilful 

 electricians, laboring to attain the result, had for six years 

 failed to make such an extension. Nor was the result by any 

 means antecedently assured by Schweigger's success with the 

 galvanometer. If Sturgeon's improvement of economizing the 

 battery size and consumption, by increasing the magnet factor 

 (in tliose few cases wliere available), was well deserving of 

 reward, surely Henry's improvement of a far greater economy, 

 by increasing the circuit factor (entirely neglected by Sturgeon) 

 deserved a still higher applause. 



In a subsequent communication to Sillimau's Journal,^IIenry 

 remarks on the results announced in October, 1821 :—" Shortly 

 after the publication mentioned, several other applications of the 

 coil, besides those described in that paper, were made in order 

 to increase the size of electro-magnetic apparatus, and to 

 diminish the necessary galvanic power. The most interesting of 

 these was its application to a development of magnetism in soft 

 iron, much more extensive than to my knowledge had been pre- 

 viously effected by a small galvanic element." The electro- 

 magnet figured and described by Sturgeon, (in his communication 

 of November, 1825,) consisted of a small bar or stout iron wire 

 bent into a U or horse-shoe form, havings a copper wire wound 

 loosely around it in eighteen turns, with the ends of the wire 

 dipping into mercury cups connected with the respective poles of 

 a battery having 130 square inches of active surface. This was 

 undoubtedly the most efficient electro-magnet then in existence. 



In June of 1828, Henry exhibited to the Albany Institute a 

 small-sized electro-magnet closely wound with silk-covered cop- 

 per wire about one-thirtieth of an inch in diameter. By thus 

 insulating the conducting wire instead of the magnetic bar or 

 core, he was enabled to employ a compact coil in close juxtaposi- 

 tion from one end of the horse-shoe to the other, obtaining 

 thereby a much larger number of circuits, and having each circuit 

 more nearly at right angles with the magnetic axis. The lifting 

 power of this magnet is not stated, though it must obviously 

 have been much more powerful than the one described by 

 Sturgeon. 



In March of 1829, Henry exhibited to the Institute a some- 

 what larger magnet, of the same character. "A round piece of 

 iron about one quarter of an inch in diameter, was bent into the 

 usual form of a horse-shoe, and instead of loosely coiling around 

 it a few feet of wire, as is usually described, it was tightly wound 

 with 35 feet of wire covered with silk, so as to form about 400 

 turns: a pair of small galvanic plates which could be dipped 

 into a tumbler of diluted acid, was soldered to the ends of the 

 wire, and the whole mounted on a stand. With these small 



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